An apparatus for analyzing a component in a sample by performing a Raman spectroscopic measurement normally includes a light source for generating the light to be cast into the sample (excitation light), an entrance optical system for converging the excitation light and casting it into the sample, a dispersing optical system for collecting the Raman-scattered light resulting from an interaction with a substance in the sample and dispersing the light into a spectrum, as well as a detector for detecting the component wavelengths of the light dispersed by the dispersing optical system.
If the intensity of the light from the sample is plotted on a graph with the wavelength as the abscissa and the intensity as the coordinate, a Raman scattering spectrum is obtained on both sides of the wavelength of the excitation light. The lines at the longer wavelengths are called the Stokes lines, and those at the shorter wavelengths are called the anti-Stokes lines.
The amount of energy corresponding to the difference between the wavelength of the excitation light and that of a Stokes or anti-Stokes line reflects the amount of energy of the natural vibration of a molecule. Accordingly, by calculating this amount of energy, it is possible to identify a substance in the sample. Furthermore, based on the intensity of each Stokes or anti-Stokes line appearing in the Raman scattering spectrum, the quantity of the substance corresponding to that Stokes or anti-Stokes line can be determined.
Patent Literature 1 discloses a gas component analyzer which identifies the components in a gas generated within a gasifying furnace and measures the concentration of each component by performing a Raman spectroscopic measurement.
FIG. 1 shows the configuration of the main components of this apparatus. In this gas component analyzer 100, laser light is cast into a stream of gas flowing in the direction perpendicular to the drawing within a tubular sample-passing unit 110 provided within the area surrounded by the broken line in a measurement chamber 115, and the Raman-scattered light emitted from the gas is measured. The laser light generated by a laser-casting device 114 controlled by a controller 137 is guided through a first optical fiber 120 into a light-casting means 116 and is converged on a predetermined position within the measurement chamber 115 by a lens 125 provided in the light-casting means 116. After passing through the gas, the laser light is disposed of at a damper 128.
Additionally, a detection optical system is provided on the wall of the measurement chamber 115 located in a direction perpendicular to the path of the laser light with respect to the aforementioned predetermined position. Among the Raman-scattered light emitted from the gas illuminated with the excitation laser light, the portion of light emitted in the perpendicular direction to the path of the laser light passes through alight-passing window 129 and is converged on a light-receiving unit 132 by a condensing lens 130. The light incident on the light-receiving unit 132 is guided through a second optical fiber 121 and is separated into component wavelengths by a light-dispersing device 135, to be eventually detected by a CCD camera 136.